Re: MinGW compilation warnings in libiberty's xstrndup.c

Pedro Alves
2017-05-19T15:22:59Z

[Adding Thomas]

On 05/08/2017 04:30 PM, Eli Zaretskii wrote:
> When compiling libiberty (as part of GDB) with MinGW on MS-Windows, I
> see the following warning:
>
> gcc -c -DHAVE_CONFIG_H -O2 -gdwarf-4 -g3 -D__USE_MINGW_ACCESS -I. -I./../include -W -Wall -Wwrite-strings -Wc++-compat -Wstrict-prototypes -pedantic -D_GNU_SOURCE ./xstrndup.c -o xstrndup.o
> ./xstrndup.c: In function 'xstrndup':
> ./xstrndup.c:51:16: warning: implicit declaration of function 'strnlen' [-Wimplicit-function-declaration]
> size_t len = strnlen (s, n);
> ^
>
> This happens because libiberty.h uses incorrect guards for the
> prototype of strnlen:
>
> #if defined (HAVE_DECL_STRNLEN) && !HAVE_DECL_STRNLEN
> extern size_t strnlen (const char *, size_t);
> #endif
>
> It should use HAVE_STRNLEN instead, because that's the only
> strnlen-related macro defined in config.g when strnlen is probed by
> the configure script.

Looks like the declaration check got added to gcc's configure, but not
elsewhere, with:

commit d968efeac356364c01445013a1a3660e5087cb15
Author: tschwinge <tschwinge@138bc75d-0d04-0410-961f-82ee72b054a4>
AuthorDate: Tue Jun 10 09:45:00 2014 +0000

[PR lto/61334] Declare prototype for strnlen, if needed.

include/
* libiberty.h [defined (HAVE_DECL_STRNLEN) &&
!HAVE_DECL_STRNLEN] (strnlen): New prototype.
gcc/
* configure.ac: Use gcc_AC_CHECK_DECLS to check for strnlen
prototype.
* config.in: Regenerate.
* configure: Likewise.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@211401 138bc75d-0d04-0410-961f-82ee72b054a4

But then, xstrndup.c has at the top:

#ifdef HAVE_STRING_H
#include <string.h>
#else
# ifdef HAVE_STRINGS_H
# include <strings.h>
# endif
#endif

So I would expect your build to pick the strnlen declaration from
one of the string.h or strings.h mingw headers. Why didn't it?

Thanks,
Pedro Alves